This invention relates generally to the problems associated with waste in animal confinements, and more specifically, to methods and systems for converting the resulting high concentrations of animal waste into useful energy.
Animals have been raised for centuries for food. Previously animals grazed in fields or pens, and were at times confined to buildings for shelter. However, current state of the art animal production for swine, cattle, and other animals, includes housing large numbers of such animals in high concentration within confined buildings, and delivering food to the animals. This method of animal production has benefited consumers of meat by lowering food prices through increased efficiency. A drawback to the current methods of animal production includes the resulting high concentration of wastes that have to be removed from the buildings and disposed of in a safe manner.
Typically, the waste is removed from animal confinement buildings and deposited into large lagoons. Once within these lagoons, which can be multi-acre in size, the waste decomposes. The solid and liquid wastes in the lagoons cause an odor problem for the surrounding area, both as it decomposes in the lagoon, and during field application as a fertilizer as further described.
After partially decomposing, the waste from the lagoons is applied to land (e.g. fields where crop are grown) as a fertilizer. The potential for environmental contamination during field application of the waste is substantial and many fields in pork producing states have been over fertilized. In addition, some of the applied fertilizer can become windborne during application and is therefore a source of environmental contamination for adjacent areas.
There are also additional weaknesses with waste lagoon technology, specifically, collapsed walls and ground leaching, both of which can contribute to waterway and well contamination. In a recent EPA report, 60% of the US streams identified as “impaired” were polluted by animal wastewater. Animal wastewater management has become a high priority for the EPA.
Still another problem with current animal production methods is that air cycled through the confinement buildings to keep the animals cool is blown into the atmosphere through the fans at the end of these confinement buildings. This is another source of airborne waste in addition to the fertilizer application problems described above. Another problem caused in part by the airborne waste is an increased susceptibility to respiratory and other health problems in farm workers. Legislative pressures have forced at least one state to impose a moratorium on new swine confinements, and other states are predicted to follow.
There have been numerous attempts to improve the current state of the art in animal production, but most of these attempts still include drawbacks. For example, some still require a waste lagoon. Another system uses an inclined belt to concentrate solids percentage of waste, but does not eliminate or gain beneficial results from the solid waste. Other systems are known in which the wastes are eliminated by burning, but the burning of such wastes is not utilized to provide a beneficial result. Other systems treat waste through chemicals, but the waste is returned to the environment as a dried sludge. Additionally, anaerobic digestion systems exist.
There are additionally several energy conversion processes known but these systems do not describe any methods for getting the waste to the conversion system, nor the overall process of handling the animal waste.